Rubber compounding



, l A colloidal solution of Patented Au 23, 1938 umrso STATES RUBBER COWOUNDING I George S. Haslan'i, Palmerton, Pa., assignor to The New Jersey Zinc Company,

New York, N. Y" a corporation of New Jersey No Drawing.

- Original application April 6, 1935,

Serial No. 15,096. Divided and this application October 31, 1936, Serial No.

8 .Claims. (01. 106-23),

This invention relatesto rubber compounding and particularly to rubber compounding in which pigments are incorporated with the rubber andhas for one of its objects the provision of an improved .method of rubber compounding.

, This application is a division of my co-pending application Serial No.-15,096,-filed April 6, 1935.

The improvedmethod of the invention com-.

' prises adding to the rubber compound as a reinforcing agent a pigment having its discrete particles coated with a proteinaceous substance.

Zinc oxide having its particles so coated may be used with special advantages in rubber compounding'. Other rubber pigments, such as whiting (calcium carbonate), blanc nxe (precipitating barium sulphate), zinc sulphide, lithopone' and more particularly crude (uncalcined) lithopone,

etc., may be advantageously coated with app'ro- 'priate proteinaceous'substances and added to the rubber compound in accordance with the invention. Theproteinaceous coating on the pigment particles is extremely thin, and the amount of proteinaceous substance associated with the pigment, substantially in the form of a coating on the individual pigment particles, is usually from about 1 to 2% byweight on the weightof pigment.

In carrying out the invention, the pigment is treated with a suitable-protein in such a manner as to coat the surface of. theparticles with asmall amount of the protein, say, i to 2% by weight. The treatment can be applied toaany pigment capable of reacting with or adsorbing the proteinaceous substance. Casein, glue, hemoglobin, egg albumen and glycine are-ex- I amples of proteinaceous substances suitable for practicing the-invention.

casein may be prepared by peptizing the casein in water in any approved manner, as, for example, as follows:

(1) Forty grams of casein are added to 600 cc. of cold water,-the temperature raised to from to C., then 12 cc. of ammonium hydroxide '(27 per cent) added. Further'heating and agi- 4 tation brings the mi ture to a state of colloidal suspension.

(2) Fifty-five grams one hour at 66 C. in then 5 grams of NaF added. After 10 minutes, 6 grams of sodium tetraborate dissolved'in 25- cc. of water .are added, and the whole mix held at 66 C. for one hQuI.

of casein are soaked for (3) Fifty grams of casein are soaked in 250 be used ,to peptize the casein. Proteins such as' 60, hemoglobin and egg albumen may be made into 250 cc. of distilled water,

be dispersed by colloidalsolutions by the same methods as casein. Proteins such as glue and glycine require no peptizing agent in the formation of the colloidal solution. The surface treatment of the pigment. with the proteinaceous substance may be conveniently efiected by mixing the pigment with a colloidal solution of the protein, prepared as indicated above, or in any other convenient manner. Thus for example the zinc oxide pigment may be mixed with the colloidal casein (or other protein) solution in such proportions that the protein added is about 1 to 2% of the zinc oxide .by weight.

The mixing of the colloidal solution with the zinc oxide pigment may be carried out as follows:

The protein solution may be sprayed on the zinc oxide pigment and mixed with the pigment by treatment in an edge runner or chaser. In opso operated the moisture .protein solution.

drying-step is necessary before tegration of the pigment, when mixing is adopted.

It is also possible to add water along with the colloidal protein solution in sumcient amounts to form a paste or slurry, containing say 50% pigment and 50% water. The paste of pigment,

introduced into the. pigment by the In consequence, no spe the final disinthis method of water and associated protein is milled'for sev-' eral hours, say four hours, and is then filterpressed. The filter-cake is then dried, say for about 36 hours, in galvanized iron oven, or other suitable heating chamber, at a temperature of from about to c. The dried filter-cake is then crushed and distintegrated in the manner customary to produce the improved dry pigment of the invention.

Protein-coated rubber pigments may be used in rubber compounding in much the same manner as the corresponding uncoated pigments. In order to improve the dispersion of the proteincoated pigment in rubber, it is desirable to disintegrate the pigment to a state of high disper-' sion. when the dried 'fllter cake obtained after the treatment of 'the pigment with protein solution is soft, the amount of disintegration on grinding requisite to produce the necessary high state of dispersion is substantially less than when the dried filter-cake is hard. A relatively soft fllterby using sodium silicate or cake may be obtained vtriethanolamine as peptizing agent in the preparation of the protein solutionwith which the pigment is treated. j

Vulcanized rubber compounds prepared with the protein-treated pigments display an increased modulusof elasticity, that is to say the load requisite to produce. a given elongation or stretch. of the rubber (say for example 300 or 500%) is increased. The abrasion resistance and tear resisttrays in ancial . good dispersion in the rubber mix (either by; masterbatching or in the .form of a colloidal suspension). The extent of the improvement by any ance of the rubber compounds are also substantially increased. In order to secure increased tear resistance, care must be taken to secure adequate dispersion of the pigment in the rubber increase can be realized by the addition of relatively small amounts (one to two per cent) if the proteinaceous material is added in a way to insure of these methods is relatively small compared with the improvement obtained resulting from the use of the protein-coated pigments. Thus, when the proteinaceous substance is applied to the pigment before incorporating the pigment in the rubber, very small amounts namely-1 0r 2% on the weight of the pigment, are sufilcient to secure an improvement greatly in excess of that obtained by the separate addition of casein or glue to the rubber compound.

The following tables indicate the improved physical properties, particularly increased modulus of elasticity, imparted to vulcanized rubber compounds by protein-coated pigments. rubber compounding formula was the same in each example. In Example 1, ordinary zinc oxide as used. In Example 2, a glue-coated zinc oxide (2% glue by weight) was used, and in Example 3,

The"

the modulus of elasticity in Examples 2 and 3 is very substantially greater than in Examples 4 and 5.

Example 4.2% Glue added to stock Load (lbs. sq. 1 Tensile P8P in.) for elonga- Time of cure in mins. at strength, cent tion of 2010s. lbs. per elon sq. in.

In the foregoing examples, the compounding formula has a fairly high zinc oxide loading parts by weight ZnO to 100 parts rubber). The following examples indicate the advantageous increase in modulus of elasticity imparted by relatively small amounts of protein-coated pigments to tread compounds where the high modulus requirements make it customary to use high carbon black content andlow zinc oxide content. In Example 6 ordinary zinc oxide was used, while in Example '7 the casein-coated zinc oxide (2% casein) was used. In Example 8, the amount of zinc oxide (coated with 2% casein) was increased to 15 parts, the added 10 parts replacing an equivalent volume 01' carbon black.

Sulphur 3 Accelerator (mercapto-benzothiaz0le) 1.25

Example 8.-Zinc aide (parts 5 by weight) a casein-coated zinc oxide (2% casein by weight) was used.

Compounding formula. Parts by weight Rubber 100 Sulphur Accelerator (mercapto-benzothiazole) 1 Stearic acid 3 Antioxidant (naphthvlamine) 1 Zinc oxide 100 Load (lbs. sq. Tensile Pep in.) for elonga- Time of cure in mine. at strength, cent tion 0i-- 20 lbs. lbs. per 6km sq. n.

Eza'mple 2.Glue-c0aed rinc wide I 3020 070 540 3440 000 035 3540 025 830 3300 006 85s 3240 B80 915 3100 use 895 Load (lbs. sq. Tensile per in.) for elonga- Time 01 cure in mins. at strength, Gent tion 0(- 20 lbs. lbs. r 61 am ong.

d zinc aside (5 parts by weight) Ezample 8.-Cauin-coated zinc wide (16 parts by weight) carbon black (36.8 parts 01 we ght) and thereafter ,ber compound.

ments, particularly. zinc oxide, treated with proteins in accordance with the invention can be advantageouslyused-with carbon black in com-'- pounding of rubber for tire treads. The known advantages resulting from high zinc oxide content are obtained thereby, with no decrease in resistance to abrasion.

I claim:

1. The improvement in rubber compounding which comprises milling a pigment with a proteinaceous substance to produce dry substantially unagglomerated pigment particles coated with the proteinaceous substance and thereafter adding said particles to a rubber compound.

2. The improvement in rubber compounding. which comprises adding to a rubber compound dry milled substantially unagglomerated pigment particles coated with a proteinaceous substance.

3.. The improvement in rubber compounding which comprises milling zinc oxide pigment with a. proteinaceous substance to produce dry substantially unagglomerated zinc oxide pigment particles coated with the proteinaceous substance dispersing said particles in a'rub- 4. The improvement in rubber compounding which comprises dispersing in a rubber compound milled dry substantially unagglomerated zinc oxwithfrom l to 2% said rubber compound.

ide pigment particles coated with a proteinaceous substance.

5. The improvement in rubber compounding which comprises milling zinc oxide pigment with a proteinaceous substance to produce substantially dry and unagglomerated zinc oxide particles coated with from lto- 2% by weight of the pigment of the proteinaceous substance, and thereafter incorporating saidparticles in a rubber com pound.

6. The improvement in rubber compounding which comprises dispersing'in a rubber compound milled substantially dry and unagglomerated pigment particles coated with from 1 to 2 %*by weight of the pigment of casein.

'7. The improvement in rubber compounding which comprises dispersing in a-rubber compound milled substantially dry and unagglomerated pig- 'ment particlescoated with from 1 to 2% by weight of the pigment of glue.

8. The improvementin rubber compounding which comprises milling zinc oxide pigment with glue to produce milled substantially. dry and unagglomerated zinc oxide pigment particles coated by weight of the pigment of glue. and thereafter adding said particles to a rubber compound and dispersing said particles-in GEORGE s. HASLAM. 

